Industrial application of motor assemblies often require that the motor be coupled to a hoist machine or overhung machine due to space limitations, industrial standards and requirements (NEMA) and the like. Such motor assemblies and applications are prevalent in the elevator industry, for example.
Existing integral overhung style elevator hoist machines were designed originally with motors having single bearings on the back end and supported in the front end by being bolted to the hoist machine. Typically, the overhung hoist machine has a sleeve bearing at the motor end with internal clearances typically of 0.005 to 0.010 inch, which is quite large. The internal clearances (i.e. movement of the shaft in an up/down fashion) of single bearing motors are compatible with these machines. However, advances in motor technology have caused the production of single bearing motors to be phased out.
New style motors such as C and D face motors are being produced and are now available from major manufacturers. These motors are consistent with NEMA standards. These new motors, which have two ball bearings, have caused the single bearing motors to become technically obsolete. Thus, the single bearing motors are no longer readily available. The new motors are manufactured with higher efficiencies which create closer tolerances and are made with ball bearings on each end in order to maintain these tolerances. Thus, the new style motors are two bearing motors, where the ball bearings used have approximately 6 microns (μm) of internal clearance when rigidly coupled to a sleeve bearing hoist machine. However, the hoist machine has over one hundred times the internal clearances of the new style motors. This causes problems when coupling the new motors to the existing hoist machines. Because the hoist machine has a much greater size relative to the internal clearances of the new style, two ball bearing motors, all of the axial and radial load is supported by the motor rather than the hoist as originally intended. Thus, if the hoist machine, which originally supported this, and has the big loading bearings therein, that bearing is rendered useless due to the closeness of the bearing in the shaft end of the motor. This results in premature bearing failure in the motor and causes end-thrusting problems associated with the encoder that is to be mounted onto the end of the motor.
In view of the above, it is highly desirable to obtain a coupling arrangement for mounting such a two bearing motor onto an existing integral overhung style hoist machine without the need for special tools or complex alignment steps and which takes into consideration proper alignment, radial overloading and end-thrusting problems that are caused when the new style motors are fitted to an older style or larger tolerance machine.